The present invention is directed to a method of processing data representing an image of an individual""s retina to identify the individual and more particularly to such a system that generates a unique and consistent signal pattern for identification of an individual from data representing the individual""s optic disk.
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Various devices are known that detect a vascular pattern in a portion of an individual""s retina to identify the individual. Examples of such devices are disclosed in U.S. Pat. Nos. 4,109,237; 4,393,366; and 4,620,318. In these devices, a collimated beam of light is focused on a small spot of the retina and the beam is scanned in a circular pattern to generate an analog signal representing the vascular structure of the eye intersecting the circular path of the scanned beam. In the 4,393,366 patent, the circular pattern is outside of the optic disk or optic nerve and in the 4,620,318 patent, the light is scanned in a circle centered on the fovea. These systems use the vascular structure outside of the optic disk because it was thought that only this area of the retina contained sufficient information to distinguish one individual from another. However, these systems have problems in consistently generating a consistent signal pattern for the same individual. For example, the tilt of the eye can change the retinal structure xe2x80x9cseenxe2x80x9d by these systems such that two distinct points on the retina can appear to be superimposed. As such, the signal representing the vascular structure of an individual will vary depending upon the tilt of the eye. This problem is further exacerbated because these systems analyze data representing only that vascular structure which intersects the circular path of scanned light, if the individual""s eye is not in exactly the same alignment with the system each time it is used, the scanned light can intersect different vascular structures, resulting in a substantially different signal pattern for the same individual.
In accordance with the present invention, the disadvantages of prior retinal identification systems and methods have been overcome. Unlike the prior art, the method of the present invention includes the analysis of bit mapped image data representing the intensity of pixels forming an image of an area of an individual""s retina that includes the optic disk. The method of the present invention locates the optic disk in the image and generates a unique and consistent signal pattern for identifying an individual from pixel data having a predetermined relationship to the individual""s optic disk. The generated signal pattern is then used to verify the identity of the individual.
More particularly, the method of the present invention finds, from the pixel data, the boundary of the optic disk in the image and generates a signal pattern from the intensity data representing pixels having a predetermined relationship with respect to the boundary of the optic disk. The signal pattern generated from the data representing the image of the optic disk is then compared to one or more stored signal patterns to verify the identity of the individual.
In accordance with one embodiment of the present invention, the boundary of the optic disk is found by fitting a circle onto the image of the optic disk represented by the pixel data and distorting the circle to fit an ellipse onto the image of the optic disk. A circle fitting closest to the image of the individual""s optic disk is found by analyzing the average intensity of the pixels within the circle and the average edge strength of the pixels positioned about the circumference of the circle as the circle""s parameters are changed to fit it onto the optic disk. The closest fitting circle is distorted into an ellipse based on the change in the average edge strength of the pixels positioned about the circumference of the ellipse as the ellipse parameters are changed.
In one embodiment of the present invention, the signal pattern identifying the individual is generated from a series of values, each value representing the average intensity of the pixels in an edge or boundary area at successive positions along the path of the ellipse fit onto the optic disk image. The average intensity of pixels associated with the optic disk and having a different relationship with respect to the boundary of the optic disk can also be used to generate a unique and repeatable signal pattern to identify an individual. For example, the area of the optic disk within the boundary can be divided into a number of sectors in which the average intensity of pixels within each sector can be used to form the signal pattern identifying an individual. Alternatively, the average intensity of the pixels at different points taken along one or more predetermined paths within the optic disk boundary or adjacent to the boundary but outside thereof can be used to form the signal pattern identifying the individual.
The method of the present invention has been found to generate a unique and consistent signal pattern to identify an individual. The method has also been found to successfully match the signal patterns generated from images of different quality to the signal pattern stored for an individual so as to provide a more reliable and robust retinal identification method than has heretofore been possible. These and other advantages and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.